We used Podio at my last employer, 3 Birds Marketing. 3 Birds is a marketing company that caters to automotive dealerships. There are multiple departments at 3 Birds and several were in need of having a good, solid project management tool to juggle multiple daily tasks. Two other colleagues and me chose Podio because of it's cost-efficiency and it's flexibility. We spent two and-a-half months building the tool to serve as a single source for internal company announcements, for projects that needed to be handed off from one department to another, and as a storage space for images and other, internally-important projects. As far as I know, the entire company is still using Podio, even after I left the company for another opportunity in August, 2013.
At 3 Birds, Podio primarily addressed two business problems: one, the lack of organization for every project and two, the clarity to see "who is working on what" at any given point in time. Prior to implementing Podio at 3 Birds, dozens of projects were sold by the sales team to the client base without checking in with the production / feasibility of the deliverables. Clients' expectations were bloating out of control and the production team(s) - namely, the writers and graphic designers - scrambled to gather details to start and deliver projects, often on the same day. The stress level was unnecessarily high. Podio addressed this - and the other challenge - who is working on what - by giving all affected teams a clear, bird's eye view of all of the projects lined-up and who they were assigned to. We built apps that represented each type of project and made many fields required in those apps. All of those apps were linked to one app, called "projects quick view" that required an assignee and a due date. The manager could then add someone to the project in projects quick view and all details had already been entered in respective apps.